The present invention relates to new and useful improvements in regenerators for industrial furnaces and especially glass melting furnaces. It is among the objects hereof to provide a method of operating a regenerator of the conventional checker tile and brick construction having a substantial array of air preheat surfaces to obtain maximum use of the sensible heat in the waste gas stream passed through the regenerator structure.
A supplemental volume of air is passed through the regenerator preheat surfaces in addition to the volume of combustion air required for the furnace fuel combustion under normal operating conditions and this supplemental volume after being heated is divided therefrom for passage to an auxiliary heat-utilizing apparatus mounted exteriorly of the furnace. The air is preheated as a unitary stream of substantial volume during its passage through the hot heat-exchanging surfaces of the regenerator and prior to diversion of at least one secondary portion to the auxiliary heat-utilizing apparatus. The heat recovery structure of the regenerator requires no modification except for providing an outlet duct for the stated secondary portion of preheated air, preferably in a region adjacent to the furnace combustion zone. Thus, the auxiliary heat-utilizing apparatus can be supplied with clean preheated air having a temperature ranging from about 1000.degree. to 2000.degree. F., for example, which can be passed through a heat exchanger and employed for power generation or other purposes without unduly penalizing furnace operating conditions.
In the system proposed, additional heat recovery from the waste gas manifests itself in the form of colder waste gas exhausting from the regenerator system. The auxiliary air stream, along with the normal combustion air stream, removes more heat from that which is stored in the regenerator refractories than would occur with combustion air only, thus cooling the storage media to colder temperatures. During the subsequent reversal of the regenerator system, the colder media are capable of absorbing more energy from the waste gas, thus exhausting the waste gas from the system at a colder temperature. The net effect is the transfer of heat from the dirt-laden waste gas stream to an auxiliary clean air stream extracted from the alternating air side of the system. A net energy savings is realized if the extracted hot air stream is delivered to a reasonably efficient heat exchanger or other heat-utilizing process or apparatus other than the combustion chamber generating the original waste gas.
Furnace waste heat recovery devices and systems normally involve insertion of heat exchangers into the waste gas exhaust stream. Deposition of particulate matter from the waste gas stream on heat-exchanger components leads to fouling and corrosion, thus requiring costly construction and soot blowing, flushing or other cleaning systems to maintain a high level of heat exchanger performance. The subject process yields auxiliary waste heat recovered without passing dirty waste gas through an auxiliary heat exchanger, thus avoiding complications associated with particulates and acids condensed from dirty furnace waste gas. The presence of the auxiliary air stream tends to yield a slight reduction in the combustion air preheat temperature. A net energy savings can be realized if the use of the extracted air stream offsets the loss of combustion air preheat energy. Many heat exchange devices readily fulfill this requirement. The subject air extraction process eliminates the problems associated with dirty furnace waste gas which tends to foul such devices and prevent their long-term continuous efficient operation.
For a regenerative glass furnace melting conventional glass batch, the combustion chamber waste gas contains more energy than can be utilized for preheating combustion air. Most of the excess energy is normally evidenced by excessively hot stack gases. The subject method consists of supplying additional or auxiliary air, in excess of combustion air requirements, to the alternating air intake side of the regenerator inlet. Together with the combustion air, the auxiliary air stream is heated by the regenerator refractory surfaces. Rather than permitting the auxiliary air stream to pass through the combustion chamber as unused excess air, the stream is extracted from the air regenerator through an opening or a series of openings in the regenerator wall leading to a duct which carries the hot air to the desired auxiliary heat exchanger. The duct extends between the two regenerators, with a "T" connected intermediate the length of the connecting duct. During operation and with the normal reversals, the combustion or air side regenerator is always at an elevated pressure while the waste gas side is always at a slightly negative pressure. The "T" connection is maintained at zero or slightly negative pressure by a stack fan so that the extracted auxiliary hot gas is always obtained from the air intake side of the system.